Single-wall carbon nanotubes (SWNTs) exhibit exceptional chemical and physical properties that have opened a vast number of potential applications. Disproportionation of CO on several bimetallic catalysts resulting in a high selectivity towards the production of SWNTs at relatively low temperatures has been shown in WO 00/73205 A1 (corresponding to U.S. Ser. No. 09/389,553) and PCT/US01/17778 (corresponding to U.S. Ser. No. 09/587,257), each of which is hereby expressly incorporated herein in its entirety and each of which may contain subject matter related to the invention claimed herein. Among the various formulations investigated therein were catalysts comprising cobalt and molybdenum (Co and Mo) supported on silica and having low Co:Mo ratios.
The Co—Mo system is previously known in the field of catalysis due to its application in hydrotreating catalytic processes. In that system, however, silica generally is not the most suitable support, due to its weak interaction with the Co—Mo components. Most studies on the Co—Mo catalysts have focused on alumina-supported systems since alumina interacts with Co and Mo with the appropriate strength to generate the HDS active species. For that reason, alumina-supported Co—Mo catalysts are used in industrial practice in the form of sulfides. Although the structure of the sulfided Co—Mo catalysts is known almost at the atomic level, that of the non-sulfided oxidic precursor has received less attention. Using IR spectroscopy of adsorbed NO showed that the interaction between Mo and the alumina in the oxidic state was not greatly affected by the presence of Co. Further, in the oxidic state, a major portion of the Co apparently is inside the alumina lattice in a tetrahedral environment of oxygen ions and is not exposed to the gas phase. However, silica-supported Co—Mo displays a different behavior from that of the alumina-supported catalysts.
It would therefore be desirable to have a detailed picture of the structure of the Co—Mo catalyst so that the silica-supported Co—Mo catalyst can be more effectively used in the production of SWNTs.
Furthermore, it would be desirable to be able to control the diameters of the SWNTs produced by the catalytic method. The diameters of the SWNTs have important implications for their thermal, mechanical and electrical properties. Control of the diameters of the SWNTs will therefore result in better control of the physical properties of SWNTs.